Polyacetylenic compounds have been used as recording layers for optical disks, digital recordings and similar information storage devices by a process calling for visually imaging the polyacetylenic film with short wavelength radiation as generated by electron beam, gamma-ray, X-ray, beta-ray, neutron particles and the like. The absorption limitations of known polyacetylenes, i.e. up to about 400 nm, excludes the economical and efficient laser imaging which is generally effected at wavelengths of about 600 nm or higher. Visual images are those images which are clearly recognizable by the human eye and are characterized by high optical contrast in one or more of the red, green and blue portions of the spectrum. High optical contrast is defined as an optical density difference of at least 1.0 between the maximum density and minimum density portions of the image, where optical density is defined as log.sub.10 (1/transmittance) for transmitted light and log.sub.10 (1/reflectance) for reflected light. Such visual imaging is significantly distinguished from prior data recording where image contrast is relatively low and not easily discernable by the human eye or without high magnification. In several cases laser imaging at wavelengths above 400 nm, based on the thermal color change of the polyacetylenic compound to develop a useful visual image, has been attempted, but it has been found that cumbersome high-output equipment, e.g. argon, metal-vapor or gas lasers and the like are required. Relatively low-output compact lasers, in the 650-1500 nm wavelength range, fail to imprint on either known polyacetylenes or their polymers, particularly in relatively thick layers required to produce useful visual images as opposed to the relatively thin layers needed for digital data recording.
A successful color imaging process for polyacetylenes with a scripting laser operating at a wavelength of 600 nm or higher has been described in copending Pat. application Ser. No. 601,537, filed Oct. 23, 1990, and entitled "Laser Imaging Composition". However, this process involves exposing a polyacetylene-dye composition to create a latent image in a first process step followed by an overall exposure with short wavelength radiation to develop a distinguishing background color of the latent image in the second stage of the process so as to provide a photonegative transmission of the original image. While highly effective, such a process requires several processing steps and is unable to generate a photopositive visual image of the transmitted pattern by exposure to a semi-conductor laser operating within desirable wavelength range of from about 600 to about 1,500 nm. Accordingly, it is the aim of research, with consideration to cost performance and production efficiency, to provide a simplified process with an organic system most suitable for visual imaging and optical data recording which is directly imageable at a laser output energy in the 600-1,500 nm wavelength range characteristic of compact semi-conductor diode lasers and which directly provides a photopositive reproduction.
It is an object of the present invention to achieve the above criteria at low cost, high performance and high production efficiency.
Another object of this invention is to provide a process for directly imaging a film to a positive, high color-contrasted transmission by exposure to semi-conductor laser emission.
Still another object of this invention is to provide a thermochromic, polyacetylenic composition which is directly polymerizable to a colored image upon exposure to a laser emission generated at relatively high wavelengths, up to about 1,500 nm.